The present invention relates to improvements in an exhaust gas purifying system for a cylinder direct injection internal combustion engine, more particularly to the improvements for achieving exhaust gas purification at a time immediately after starting of the engine.
In order to purify exhaust gas discharged from an automotive internal combustion engine, a catalytic converter including a catalytic element has been hitherto used to be disposed in an exhaust gas passageway of the engine. The catalytic element carries catalyst components such as noble metals (platinum, palladium, rhodium and the like) or other metals. Under the catalytic action of such catalyst components, HC (hydrocarbons), CO (carbon monoxide), NOx (nitrogen oxides) and the like as noxious components in exhaust gas are oxidized or reduced to be converted to harmless gases. Now, it is necessary to raise the temperature of exhaust gas and accordingly the temperature of the catalytic components in order to effect the catalytic action of the catalytic components. For example, it is necessary to raise the temperature of the catalyst components to 200 to 300xc2x0 C. in order to effect the catalytic action for oxidizing HC. However, at a time immediately after starting of the engine, the temperature of exhaust gas is low and therefore cannot reach a level (for example, above 200xc2x0 C.) for activating the catalyst components, so that oxidation of HC is hardly accomplished. As a result, an amount of HC emitted to the atmosphere will increase.
In view of the above, in order to solve the above-discussed problems, a variety of techniques have been hitherto proposed as disclosed in Japanese Patent Provisional Publication Nos. 6-241028, 7-144119, 9-256840 and 8-296485.
Of the above conventional techniques, one disclosed in Japanese Patent Provisional Publication No. 8-296485 is arranged as follows: In a cylinder direct injection internal combustion engine in which fuel is directly injected from a fuel injector valve into an engine cylinder, additional fuel is injected from the fuel injector valve into the engine cylinder in or after expansion stroke of the engine, so that the additional fuel is mixed in its unburned state with air and supplied to an exhaust system so as to be burned around a catalytic element thereby smoothly raising the temperature of catalyst component in the catalytic element.
However, in this conventional technique, there is the fear that the additional fuel cannot be sufficiently burnt, for example, at a time immediately after engine starting at a low temperature. At such a time, the temperature of an exhaust port, an exhaust manifold, an exhaust pipe, and a catalytic converter which form parts of an exhaust gas passageway is low. Accordingly, not only exhaust gas cannot be heated, but also the additional fuel is unavoidably discharged to the atmosphere.
It is, therefore, an object of the present invention to provide an improved exhaust gas purifying system for an internal combustion engine, which can effectively overcome drawbacks encountered in similar conventional exhaust gas purifying systems for internal combustion engines.
Anther object of the present invention is to provide an improved exhaust gas purifying system for an internal combustion engine, which can securely and smoothly raise the temperature of a catalyst component in a catalytic converter and activate the catalyst component, thereby effectively reducing unburned HC emitted to the atmosphere without being equipped with any special exhaust gas heating apparatus.
A further object of the present invention is to provide an improved exhaust gas purifying system for a cylinder direct injection internal combustion engine equipped with an adsorbent catalytic converter having a HC adsorbent, in which additional fuel can be injected from a fuel injector valve into an engine cylinder in case that unburned hydrocarbon adsorbed in the adsorbent is to release before activation of a catalyst component of the catalytic converter with a temperature rise after engine starting at a low temperature.
An aspect of the present invention resides in an exhaust gas purifying system for an internal combustion engine having a fuel injector valve for directly injecting fuel into a combustion chamber of the engine. The exhaust gas purifying system comprises an adsorbent catalytic converter disposed in an exhaust gas passageway of the engine, the adsorbent catalytic converter including a catalytic element having an adsorption layer. The adsorption layer contains an adsorbent which is able to adsorb HC (hydrocarbons) of exhaust gas in a first temperature range and to release the adsorbed HC in a second temperature range higher than the first temperature range, and a catalyst component for promoting reaction for oxidizing HC which is released from the adsorbent. A control unit is provided to be programmed to carry out (a) judging that a temperature of the adsorption layer reaches a releasing level relating to the second temperature range, so as to make a first judgment result; (b) judging that a temperature of exhaust gas flown into the adsorbent catalytic converter will rise upon injection of an additional fuel from the fuel injector valve into the combustion chamber during a time period including an expansion stroke and an exhaust stroke of the engine, so as to make a second judgment result; and (c) causing the fuel injector valve to controllably inject the additional fuel during the time period including the expansion stroke and the exhaust stroke of the engine upon making both the first and second judgment results.
Another aspect of the present invention resides a process for purifying exhaust gas from an internal combustion engine having a fuel injector valve for directly injecting fuel into a combustion chamber of the engine, and equipped with an adsorbent catalytic converter disposed in an exhaust gas passageway of the engine. The adsorbent catalytic converter includes a catalytic element having an adsorption layer. The adsorption layer contains an adsorbent which is able to adsorb HC (hydrocarbons) of exhaust gas in a first temperature range and to release the adsorbed HC in a second temperature range higher than the first temperature range, and a catalyst component for promoting reaction for oxidizing HC which is released from the adsorbent. The process comprises (a) judging that a temperature of the adsorption layer reaches a releasing level relating to the second temperature range, so as to make a first judgment result; (b) judging that a temperature of exhaust gas flown into the adsorbent catalytic converter will rise upon injection of an additional fuel from the fuel injector valve into the combustion chamber during a time period including an expansion stroke and an exhaust stroke of the engine, so as to make a second judgment result; and (c) causing the fuel injector valve to controllably inject the additional fuel during the time period including the expansion stroke and the exhaust stroke of the engine upon making both the first and second judgment results.